The invention relates to a solenoid valve, which has an electromagnetically actuated valve rod. The valve rod can be deflected starting from a first switching position into a second switching position.
Solenoid valves which can be electrically actuated are used, for example, for switching coolant circuits in cooling systems of motor vehicles. Such valves can assume stable switching positions in the respective end positions thereof (i.e. degenergized or energized), whereby “digital” switching operations can be achieved. Known solenoid valves have a deflectable valve rod, on which a ferromagnetic armature and (at least) one closing element in the form of a sealing cone are disposed. By energizing a field coil, the armature and an associated ferromagnetic opposite pole can be magnetized, whereby a force of attraction between said components and thereby a deflection of the valve rod starting from a first switching position into a second switching position can be brought about. The closing element disposed on the valve rod can thereby be moved into a valve seat or be removed from the same. With the aid of a return spring and/or as a result of the hydraulic pressure of a coolant, the valve rod can again return back into a first starting position when power is switched off to the solenoid valve. Valves working according to this principle, which are available as a normally open valve or as a switching valve, are described in the German patent specification DE 197 54 257 A1, the European patent specification EP 0 653 990 B1 and the German patent specification DE 197 53 575 A1.
A disadvantage of conventional solenoid valves is a relatively high, permanent current consumption in the energized switching position. The use of a cut-off valve in a vehicle cooling system can, for example, require a closing force in the range of 20N in order to hold the valve closed against the force of the return spring and against the hydraulic pressure. In the case of an on-board voltage of 12V, this can be associated with a permanent current consumption in the range of 1 A. Because no mechanical work is performed in the closed valve state, the electrical power in the field coil of the valve is completely converted into heat. This power loss makes it difficult to use such a cut-off valve in modern, efficiency-optimized vehicles. The dimensioning of the coil is also substantially determined by the aforementioned thermal boundary condition.
In contrast, solenoid valves have the advantage of behaving reliably in the event of a fault (fail-safe function) because the valves independently switch into a stable, secure switching position (for example: open) when a loss of the electrical power supply occurs (for example as a result of contact interruption, voltage drop, cable breakage, plug separation, etc.). In the case of valves which are designed differently and in which there is no electrical power consumption in stable switching positions, said fail-safe function cannot be realized to date or can only be implemented with the aid of auxiliary mechanisms (which in turn are associated with a high permanent current consumption). For that reason, solenoid valves continue to be widely used in motor vehicle cooling systems despite the high power electrical power loss associated with the use thereof